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1.
This paper presents a transient mathematical model of the HVDC converters-Equivalent Circuit Method(ECM), which can describe all possible states of converter valves in a simple and explicit way. With the converter model, programs have been implemented for single and double bridge HVDC systems. The results of simulation to the normal and fault operation of HVDC system show that the method is flexible and reliable, and has the advantages of small calculation amount and less computer storage requirments. The programs based on this paper provide convenient, inexpensive and feasible tools for computer dynamic or transient analysis of the HVDC systems. 相似文献
2.
Zhang Wei Ren Zhen 《保鲜与加工》1988,(6)
After considering the features of the differential equations which have described the dynamic behaviours of HVDC systems, a fast algori -thm is presented for these equations. Compared with the fourth Runge-Kutta Method,this method has less amount of calculation with the same precision, numerical stability and other properties. Therefore, the use of the method has greatly increased the speed of the digital simulation of HVDC systems.In this paper an example of calculation is given, and the results obtained hv using this example are compared with the results obtained by calculating with the fourth Runge-Kutta Method. The speed of simulation by using this method is about 1.8 timss as fast as that by using the fourth Runge-Kutta Method. 相似文献
3.
NPV have been widely applied. A majority of the existing calculating methods of cash flow are the static method or the expectation method. It is more reasonable to regard future cash flow as random variable which has certain probability distribution, which shifts with time. But the research about it has been introduced rarely. Through introducing some kinds of existing methods and considering the feature of Markov method, a dynamic method which is used in solved the distributing of indeterminate feature cash flow is showed. So a new kind of dynamic calculation method about NPV is obtained. The method is applied in the calculation to future cash flow of the certain highway investment project of China. The result shows that this method is feasible, effective. 相似文献
4.
Founding the mathematic model of refrigeration system's dynamic process is the basis of realizing the optimal control of refrigeration machines.Refrigeration evaporator is a kind of two-phase flow and heat exchange with complex process.For its obvious nonlinearity and uncertainty,it is difficult to describe by accurate theoretical model.This paper partitions the input data into some clusters by entropy method and competitive learning algorithm,then the on-line fuzzy identification of dynamic process mathematical model of evaporator is achieved by utilizing ultimate parameter which is ascertained by the recursive least-square(RLS).The simulation results show that fuzzy identification method is effective for on-line model process of evaporator in refrigeration system.The model has not only superior identification precise,but also quite perfect generalizable performance and traceable ability. 相似文献
5.
Under multi-support earthquake excitation, the damping is proportional to the relative velocity in relative motion method, While the damping is proportional to the absolute velocity in method of direct solving absolute displacement, and the damping assuming difference may cause the calculation errors on structural responses. The structural response errors of the dynamic component of power spectral density between the two solving methods are derived by random vibration theoretical analysis in Rayleigh damping model, which include damping ratio and the ratio between excitation frequency and fundamental frequency of the structures. Based on probability theory, the variation errors of dynamic component response between the two solving methods are also derived by theoretical analysis, and some numerical examples are provided to verify the error analysis. At last, it is pointed out that the calculation errors between the two solving methods decrease with damping ratio, and it is negligible when the damping ratio of structure is less than 5%. 相似文献
6.
Based on the calculation procedure of dynamic coordinate method, the examples in this paper prove, that the first-order stress of thin-wall member is easily calculated with the new method and that a new method of first-order analysis is easily comprehended. 相似文献
7.
The Object-Oriented technology is introduced into the 3-d Numerical Manifold method(NMM). The design method and management of the Classes about the three dimensional Numerical Manifold Method are studied. The Classes are designed and the prototypes of some key classes are shown. As an example,the 3-d numerical calculation results are given. The calculation results are in good agreement with the theoretical solutions. It shows that the Object-Oriented programming of 3-d NMM is correct. 相似文献
8.
The reproducing kernel particle method (RKPM) is a typical meshless method based on kernel function simulation. Based on the interpolating shape function of RKPM and Mindlin plate theory, the governing equations of RKPM to the deflection solution of Mindlin plate bending on a Winkler elastic soil foundation are established. Numerical results indicate that the above method and the corresponding program are effective and accurate. 相似文献
9.
In elastic mechanics, it is common practice to calculate critical loads in buckle of thin plates by means of double triangle series. The calculation process is more complex, this method has not facility in engineering application. In many cases critical loads of thin plates can not obtain precise analytic solutions. It is very important to solve approximate resolutions of critical loads of plates in engineering. The method of weighted residuals is an available measure to solve proximal resolutions of differential equations and has extensive application in egineering. In order to simplify calculation process and obtain profitble result, by means of method of weighted residuals and Cantorovich variational principle, taking the second Tchebychev's polynomials as trial functions, it was calculated, critical loads of rectangle thin plates in different supporting conditions. Calculation results indicate that this calculation method is simple and has some precision, it is applied conveniently in engineering. 相似文献
10.
This paper presents a dynamic hybrid substructure synthetic method for tower crane dynamic analysis. This method employs the transfer matrix method and the flexibility degree method respectively to formulate the vibration mathematical models of the tower body and tower top system substructures in the hoisting luffing plane. Based on the motion of the substructures in the interface and the dynamic harmonize condition, the frequency equations are established. Then the program is designed according to the mathematical models and firstly applied to the dynamic analysis of the QTZ63 tower crane in the construction site and the parameter identification of attached device and tower body. The test results show that the value calculated by the above method is quite approximate to the instrument measured value, which can meet the engineering requirements. Further study has found that , for the flexible long-distance attached tower crane, the method that introduces dynamic load coefficient for statics analysis of tower cranes is unprecise enough since there exist errors.This paper suggests to conduct site test and identification of the rigidity coefficient of attached device of the tower crane for the accident prevention of tower crane collapse by timely take measures. 相似文献
11.
Monolayer cable net system for point - supported glass facade is a kind of flexible tension structures with relatively strong nonlinearity. Its stiffness greatly depends on the pretension in cables. Yet there are few literatures at present reported on its dynamic properties. The characteristic of modal analysis for flexible pre - stressed structures such as cable structures is expatiated herein. Corresponding program was developed to analyze two important factors such as pretension and geometric nonlinearity for dynamic behaviors of cable net herein. It is demonstrated that large errors are brought about by omitting nonlinearity. There exists apparent nonlinear relationship between vibration frequency and pretension in cables. The influence of pretension and geometric nonlinearity on the dynamic properties of cable net is in coordination with each other. 相似文献
12.
There are a lot of influencing factors of land price. Method of t-test of regression analysis model can be used to conduct the analysis of significance of influencing factor of land price. In the case of small sample or indefinite error distribution, there is a problem of unlikelihood of statistical referrer. So that, introduce Bootstrap method in the model to increase precision of estimated variance of parameters and reliability of statistical referrer of significance of influencing factor. Take an empirical analysis based on the data of land deal of Chongqing. The result indicates that it is very efficient to solve such problem by Bootstrap method. 相似文献
13.
In this article, modal analysis technology about dynamic analysis was studied. Free interface model comprehensive method was used to dynamic analysis and design of automobile structure based on theory background of model analysis, test technology conditions, data reliability and precision. In order to test the efficient and possibility of the method, main vibration features about space double layer has been calculated based on this method, comparing this with the precise solution of finite element method, the result shows that this method is suitable not only for simple interfaces between components but also for high reductive interfaces. In addition, the method also has high comprehensive precision. Furthermore it creates conditions to dynamic analysis in automobile structures. 相似文献
14.
In mechanical design and application, in order to calculate torsion angle and shear stresses of prismatic bars with seetorial cross-section undergoing extemal couples, the numerical method is presented. The torsion equation is nonhomogeneous partial differential equation. First, using the method of separation of variables, torsion stress function is acquired in polar coordinate. Then, the method of boundary collocation is improved to calculate the undetermined parameters. Finally,approximate numerical solutions of stress function and shear stresses in cross-section are obtained. It is given the several calculation results of shear stresses of prismatic bars with different vertex angles. These results show that the method has some precision and application feasibility in engineering design. The method of separation of variables is combinied with the method of boundary collocation simplified calculation process. 相似文献
15.
SBR method is the short for intermittent sequencing batch freatment that is an ideal techmology to order a certain amount of intermittent operation of the activated sludge treatment process. SBR which is currently an in-depth study of the biological wastewater treatment technology is a simple process, the effect of stability, small footprint, and strong resistance to shock load and has good advantages of nitrogen and phosphorus removal capacity. This study first analyzes and discusses substrate degradation process of SBR method , compares among several different SBR methods, and then derives microbial growth and substrate degradation kinetics relationship with a view to promoting the progress of the work in this area. 相似文献
16.
Through the analysis of the equivalent resistance method, a limitation of the equivalent capacity method was presented. When the direction of power at the feeder source end was changing, the equivalent capacity method for handling small generations would produce a large power loss calculation error. An improved calculation method, one not based on a single equivalent resistance, was proposed. In this method, one day was divided into several periods (such as 24 h), so that the direction of power at the feeder source end for each period does not vary. The equivalent resistance and energy loss in each period were calculated. The sum of all energy losses provided the daily energy loss total. Numerical examples were used to verify the improved method. 相似文献
17.
Rock is a kind of physical nonlinear complicated medium, under deep buried condition the surrounding rock system deformation shows geometrical nonlinear characteristic, and the interaction between the two nonlinear mechanism makes the unloading of surrounding rock system evolving complexly. Based on the Lagrangian method and large deformation caculation method, both the double nonlinearity and nonlinear dynamics character of deep buried tunnel surrounding rock system under unloading are studied. The numerical model results show that the Kolmogorov entropy has been extracted from the evolution data in the unloading process of surrounding rock system. The analysis indicates that the typical chaos character has been demonstrated in the process of unloading for deep buried tunnel surrounding system and the rock mass energy dissipation is analyzed at the stage of unloading. 相似文献
18.
The iterative Lanczos-reduce method for sensitivity analysis, the Guyan condensed method and the iterative synchronous vector methods in finite element modal are studied in order to solve the dynamic characteristic of complicated machine system. The primary reasons influenced on calculation precision are pointed out. The principia of master freedom for Guyan condensed method are put forward. The calculation precision of three methods is compared with the same standard finite element model. The iterative Lanczos-reduce method for sensitivity analysis is proved to be optimum analysis and the eigenvalue of arm in work device of hydraulic excavator in finite element model is solved with iterative Lanczos-reduce method for sensitivity analysis. The theory basis is provided for reasonable choose to solve the dynamic of complicated machine structure. 相似文献
19.
YANG You fa 《保鲜与加工》2002,(1):13-18
Based on the principle of the foundation coefficient " m-k " method,the ginite difference method is presented to analyze the internal forces of a whole prestressed anchor stabilizing pile. The calculation and figure treatments are programmed. An example shows that the high precise solution can be obtained if the segments are small enough, though more computing time may be consumed. Obviously,the calculation precision is better than that of traditional method. The results of figure treatments by the program can optimize the construction design of stabilizing piles. Three kinds of support condition are taken into account.The foundation coefficient "m-k " method applies to the situation that above the slide-surface is soil layer or efflorescence layer,while below the slide-surface is terrane. 相似文献
20.
To overcome the disadvantages of general networks such as slow convergence speed and being unable to combine with the expert knowledge etc,the authors introduces compensatory fuzzy neural cells,integrate the powerful knowledge expressiveness of fuzzy system and the excellent self-learning of neural network,and present a novel Compensatory Fuzzy Neural Network(CFNN) based on Adaptive Learning Rate Method which changes the learning rate using Adaptive Learning Rate Method in dynamic way.Finally this method is applied to the actual case.The result proves that it not(only) can adjust parameters properly on line,but also can optimize relevant fuzzy reasoning in dynamic way,fasten training rate. 相似文献